Patients who suffer from the pain and immobility caused by osteoarthritis and rheumatoid arthritis have an option of joint replacement surgery. Joint replacement surgery is quite common and enables many individuals to function properly when it would not be otherwise possible to do so. Artificial joints are usually comprised of metal, ceramic and/or plastic components that are fixed to existing bone.
Such joint replacement surgery is otherwise known as joint arthroplasty. Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged joint is replaced with a prosthetic joint. In a typical total joint arthroplasty, the ends or distal portions of the bones adjacent to the joint are resected or a portion of the distal part of the bone is removed and the artificial joint is secured thereto.
There are known to exist many designs and methods for manufacturing implantable articles, such as bone prostheses. Such bone prostheses include components of artificial joints such as elbows, hips, knees and shoulders.
Currently in total hip arthroplasty, a major critical concern is the instability of the joint. Instability is associated with dislocation. Dislocation is particularly a problem in total hip arthroplasty.
Factors related to dislocation include surgical technique, implant design, implant positioning and patient related factors. In total hip arthroplasty, implant systems address this concern by offering a series of products with a range of lateral offsets, neck offsets, head offsets and leg lengths. The combination of these four factors affects the laxity of the soft tissue. By optimizing the biomechanics, the surgeon can provide a patient a stable hip much more resistant to dislocation. In order to accommodate the range of patient arthropometrics, a wide range of hip implant geometries are currently manufactured by DePuy Orthopaedics, Inc., the assignee of the current application, and by other companies. In particular, the S-ROM® total hip systems offered by DePuy Orthopaedics, Inc. include three offsets, three neck lengths, four head lengths and one leg length adjustment. The combination of all these biomechanic options is rather complex.
Anteversion of a total hip system is closely linked to the stability of the joint. Improper version can lead to dislocation and patient dissatisfaction. Version control is important in all hip stems. However, it is a more challenging issue with the advent of stems with additional modularity.
The prior art has provided for some addressing of the anteversion problem. For example, the current S-ROM® stems have laser markings on the medial stem and the proximal sleeve. This marking enables the surgeon to measure relative alignment between these components. Since the sleeve has infinite anteversion, it is not necessarily oriented relative to a bony landmark that can be used to define anteversion. In fact, the current sleeves are sometimes oriented with the spout pointing directly laterally into the remaining available bone.
Prior art stems may be aligned relative to a patient's bony landmarks. These stems are monolithic. They cannot locate the neck independently of the distal stem. Therefore, the anteversion is limited. Most bowed, monolithic stems are sold in fixed anteversion; for example, at an anteversion of 15 degrees. These monolithic stems have limited flexibility for rotational alignment since the distal stem must follow the bow of the patient's femur and this may not provide an operable biomechanical result.
In a common step in the surgical procedure known as total hip arthroplasty, a trial or substitute stem is first implanted into the patient. The trial is utilized to verify the selected size and shape of the implant in situ on the patient and the patient is subjected to what is known as a trial reduction. This trial reduction represents moving the joint, including the trial implant through selected typical motions for that joint. Current hip instruments provide a series of trials of different sizes to help the surgeon assess the fit and position of the implant. Trials, which are also known as provisionals, allow the surgeon to perform a trial reduction to assess the suitability of the implant and implant's stability prior to final implant selection. In order to reduce inventory costs and complexity, many trialing systems are modular. For example, in the Excel Instrument System, a product of DePuy Orthopaedics, Inc., there is a series of broaches and a series of neck trials that can be mixed and matched to represent the full range of implants. There is a single fixed relationship between a broach and a neck trial, because these trials represent a system of monolithic stem implants.
Likewise, in the current S-ROM® instrument systems provided by DePuy Orthopaedics, Inc., there are neck trials, proximal body trials, distal stem trials, head trials and sleeve trials. By combining all these components, the implant is represented. Since the S-ROM stem is modular and includes a stem and a sleeve, the angular relationship or relative anteversion between the neck and the sleeve is independent and represented by teeth mating between the neck and the proximal body trial. The proximal body trial has fixed transverse bolts that are keyed to the sleeve in the trialing for straight, primary stems. The long stem trials do not have the transverse bolts and are thus not rotationally stable during trial reduction and therefore are not always used by the surgeon.
With the introduction of additional implant modularity, the need for independent positioning of the distal stem, proximal body and any sleeve which comprise the implants is required. Currently bowed, monolithic stems are offered with a fixed amount of anteversion, typically 15 degrees.
Thus, a need for a prosthetic trial and related implants that provide for anteversion alignment relative to a patient's bony landmark exists.